1. Field of the Invention
The present invention relates to antistatic polyester fibers. More particularly, the present invention relates to hollow antistatic polyester fibers consisting of a single component and in which antistatic agents are dispersed in a high density around the hollow of the fiber.
2. Description of the Prior Art
Synthetic fibers the typical example of which is a polyester fiber are superior in various properties, such as mechanical strength, durability and function, to natural fibers. However, the polyester fibers have a fatal disadvantage in that they are liable to charging with static electricity because of their high electrical resistance.
Various methods have been heretofore proposed to prevent the synthetic fibers from being charged with static electricity. However, these methods all have advantages and disadvantages. That is, it is the state of the art that the conventional methods are not completely satisfactory in respect of yarn-making cost, antistatic property and durability thereof, and the physical properties of the resultant fibers. The simplest conventional method comprises spreading or applying an antistatic agent on the surface of the fiber. This method is disadvantageous in that the antistatic agents deposited on the surface of the fiber are liable to be removed during the dyeing step or repeated washings, and thus, a permanent antistatic property can not be imported to the fiber.
If focus is directed only to the antistatic property of the synthetic fibers, the durability of the antistatic property is a basic requisite. In this sense, it can be stated that a preferable method for rendering the synthetic fibers antistatic is to incorporate antistatic agents into the synthetic resins from which the fibers are made before spinning. In this regard, the following means are well known. That is, (a) Japanese Patent Application Publication No. 39-5214 discloses incorporating uniformly a polyoxyalkylene glycol into synthetic resins; (b) Japanese Patent Application Publication Nos. 47-11280, 46-22200 and 47-10246 disclose incorporating a mixture of a polyoxyalkylene glycol and sodium alkylbenzenesulfonate into synthetic resins and (c) Japanese Patent Application Laid-open No. 53-149247 discloses incorporating a mixture of a polyoxyalkylene glycol and a sodium alkyl sulfonate into synthetic resins. These publications generally recommend that the antistatic agents are used in amounts of 2% by weight or more ((a)), from 0.7 to 8% by weight ((b)) and from 1.0 to 2.0% by weight ((c)), respectively. It is necessary, however, to use a relatively large amount of the antistatic agent in order to attain a practical antistatic effect. That is, the method (a) requires 6% by weight or more; the method (b) about 7.5% by weight and the method (c) 3% by weight, as disclosed in the respective examples. The use of such a large amount of the antistatic agent results in not only the deterioration of the mechanical properties of the resultant fiber itself, but also a reduction in fastness when the fiber is dyed. In addition, the conventional antistatic agents inevitably have a high affinity to water. Accordingly, when a knitted or woven fabric made from the fibers resulting from the above mentioned methods is subjected to a scouring, dyeing or washing procedure involving the use of water, the antistatic agents present in the interior of the fiber are dissolved out from the surface of the fiber, which results in a rapid decrease in the antistatic property of the fabric for this reason, in practice, it is necessary to use the antistatic agent in amounts large enough to compensate for such loss, which results in an increasing deterioration in the physical properties of the resultant fiber.
Among the decreased physical properties of the fiber, a most serious disadvantage which can not be overlooked is the fibrillation of the fiber which is high in the polyester fibers. This phenomenon is due to the fact that the polyester fiber essentially has a poor compatibility with the antistatic agent. In particular, when the amount of antistatic agent used is about 4% by weight or more, the resultant fiber is liable to be fibrillated and this propensity is further provided by mechanical action exerted on the fiber.
In order to prevent the deterioration of the physical properties of the fiber, a composite spinning method for preparing a core-in-sheath type fiber is known. In this method, at least two types of polymers are used. The sheath component comprises a homopolymer, while the core component comprises the same or a different polymer containing a large amount of an antistatic agent, a polymer containing a significant amount of an electric conductive material such as carbon or metals, or a polymer which has undergone a high degree of chemical modification. In this type of fiber, even if the amount of antistatic agent used is decreased, an excellent antistatic property can be obtained without having an adverse effect on the mechanical properties and dyeing property of the fiber. However, as has been previously indicated, this method has a great disadvantage in that it is remarkably costly to prepare the fiber, which makes it impossible to put it to practical use.
Notwithstanding that a number of methods for rendering the synthetic fibers antistatic, such as the spreading method, the incorporating method and the composite spinning method, have been proposed since the appearance of the fibers, none of these methods could have simultaneously satisfied the above mentioned requirements such as the practical level of antistatic effect, and the durability thereof; the high mechanical strength, resistance to fibrillation, excellent dyeability and low cost of yarn-making.